Just how much of an error are we discussing here? If it's only a millimeter here and there then you won't notice a thing. But if we're taling a lot more than it'll likely have some minor impacts. But if it's more than a couple of millimeters here and there you really need to work on your craft skills or CAD skills.

One place small differences will hurt you is the critical areas like the wing leading edges. But a template or other jigs to control the shaping can be used to help out.

As for setup angles of the wing to tail surfaces you'll want to be within a degree of square and within a few millimeters of symetry in span and chord. But if the elevator hinge line is out by 2 or 3 degrees it won't affect the flying much. Same if a fin is tilted slightly to the side. But if that same fin isn't alinged to the centerline to within a degree then you'll have some unwanted effects. Same with the wing to stabilizer angles.